The present invention relates to a shutter mechanism for cameras and, more particularly to a shutter mechanism of the type having at least one shutter blade urged by a spring and two electromagnetic means by which the shutter blade is held in and is returned to its blocking position.
Investigations from the standpoint of miniaturizing cameras without distinctions as to cameras equipped with either lens shutters or focal plane shutters has been carried out. In a miniature camera of the type having a lens shutter it is one of the leading features of camera sysytems to provide shuck such a camera with a motor powered film winding mechanism, a flash illumination unit and/or an automatic focusing apparatus built therein and thus, it has become one of essential aims in camera design to reduce the number of camera parts in order to provide miniturized cameras with various functions available. With these points as background, constructions including a shutter mechanism have been greatly simplified. However, there is much room for further improvement. For example, in conventional typical electrically controlled shutter mechanisms, an opening shutter blade is brought into engagement with a mechanical cocking member by a film transport mechanism against the force of spring means by which the opening shutter is urged toward unlocking position in which an exposure aperture is opened and thereby, held in its blocking position. When a shutter release member permits the cocking member to disengage with the opening blade, the latter is caused to move to its unblocking position to initiate exposure. At the same time, a retarding means which takes the form of electromagnetic means is actuated to retard a closing shutter blade in its unblocking position. Immediately after an exposure time automatically selected by an exposure control circuit, the retarding means is deactuated to cause the closing blade to move to its blocking position, resulting in the termination of exposure.
One of the problems associated with the shutter mechanism above described is concerned with a self-cocking mechanism by which a tension spring is urged to cause a shutter blade to move as well as to cause the loaded film to be moved by one frame. The provision of such self-cocking mechanism makes cameras bulk, due to the number of camera parts. Furthermore, if a camera with a motor powered film winding mechanism built therein is subjected to a self-cocking function, there is a disadvantage that too much load is put on the motor which is powered by a battery with a limited capacity.
On the other hand, there has been proposed another shutter mechanism of the type having electromagnetic means such as a solenoid for opening and closing the shutter. Although this type of shutter is favorable in view of its simplified mechanical linkage and the reduced number of camera parts, there still remains the disadvantage that it is required to supply too much electric energy to the electromagnetic means, or to scale up or specialize the shape of the electromagnetic means because of the fact that the shutter is to be caused to instantaneously open and close by great electromagnetic driving force. This is also disadvantageous in view of battery capacity, compactness and cost.